Terminal assembly for electric fuses



O t 1955 'r. E. CURTIS EFAL TERMINAL ASSEMBLY FOR ELECTRIC FUSES Filed Feb. 25, 1953 ll W N S III R H n m m m 0 3 2 m W A WM 5% HE VI W A B J 6 Q United States Patent 2,721,242 TERMINAL ASSEMBLY FOR ELECTRIC FUSES Thomas E. Curtis, lampton, and James M. de Montmollin, Griffin, Ga., assignors to Southern States Equipment Corporation, a corporation of Georgia Application February 25, 1953, Serial No. 338,836 Claims. (Cl. 200-127) This invention relates to terminal assemblies for electric fuses and more particularly to an improved pressure relieving terminal assembly for use in conjunction with power fuses and cutouts.

Fuses must be capable of interrupting a wide range of currents and, when constructed so as inherently to be capable of interrupting currents of a low order of magnitude, may be damaged when called upon to interrupt currents of a high order of magnitude. For example, a fuse in which the fuse tube is constructed of material which emits gas when in close proximity to an electric arc may be ruptured when interrupting excessive currents since the rate of gas emission is a function of the current magnitude.

In known constructions the button head of a fuse element is arranged with respect to its terminal assembly so as normally to close an exhaust passage, and means for frictionally gripping the button head are provided to maintain the button head in its normal position thereby to keep the exhaust passage closed. When suflicient pressure builds up within the fuse tube due to the formation of an arc therein of predetermined current magnitude, the button head is blown completely out of its terminal assembly.

One object of this invention is to provide an improved pressure relieving terminal assembly which is simple in construction and which affords a high degree of safety insofar as operating personnel are concerned.

Another object of this invention is the provision of a protective enclosure for shielding vulnerable pressure relieving parts of a fuse terminal assemblyv from the heat given off by electric arcs formed within the associated fuse tube during a circuit interrupting operation.

A further object of this invention is to provide a fuse terminal assembly which utilizes a fuse button head as a pressure relieving device and which retains the button head therein during a circuit interrupting operation.

Still another object of this invention is the provision of pressure relieving structure for power fuses which is readily adjustable so as to vary the internal pressure threshold at which the pressure relieving structure operates and so as simultaneously to vary the rate at which the pressure gas is exhausted to atmosphere.

A still further object of this invention is to provide an improved electric fuse which is readily refused after an interrupting operation.

The invention in one form as applied to a fuse cutout comprises a terminal element having a main passage in communication with an exhaust passage, closure means normally positioned to prevent internal communication between one end of the main passage and the exhaust passage, and yieldable means arranged so as normally to bias the closure means toward its normal position. Upon the occurrence of pressure within the fuse tube of the cutout which is in excess of a predetermined value, the closure means moves from its normal position to an operated position within the confines of the terminal assembly to allow the pressure gas to exhaust to atmosphere through the exhaust passage and to isolate and shield the yieldable means from the heat of the are.

For a better understanding of the invention reference may be had to the following description taken in conjunction with the accompanying drawing in which Fig. l is a side view of a dropout cutout embodying the invention and in which Fig. 2 is an enlarged cross-sectional view of a terminal assembly for the cutout of Fig. l constructed according to the invention.

With reference to Fig. l the numeral 1 designates a metallic support arm which is aflixed to a crossarm or other structure (not shown) at its left-hand extremity. Insulators 2 and 3 are supported by arm 1. Afiixed to the upper end of insulator 2 is a terminal bracket 4 to which the circuit conductor 5 is secured by means of the longitudinally split terminal bolt 6. A hood 7 is pivotally mounted to the terminal bracket 4 by a pin 8 and is biased for clockwise movement about pivot 8 by means of a spring element 9 which is secured by any suitable means to the terminal bracket 4 at its right-hand extremity and which engages the left-hand portion of the hood 7. Hood 7 is provided with a latching surface 10. A brush contact 11 mounted on terminal bracket 4 cooperates in known manner with the cutout terminal assembly generally designated by the numeral 12. Terminal assembly 12 is afiixed to the upper end of the fuse tube 13 while the terminal assembly generally designated by the numeral 14 is affixed to the lower end of the fuse tub 13.

Secured to the lower end of the insulator 3 is a terminal bracket 15 to which the circuit conductor 16 is connected by means of the longitudinally split terminal bolt 17. Terminal bracket 15 comprises a pair of laterally spaced support elements 15a which are provided at their right-hand extremities with a slot or notched portion 18 and between which a yieldable contact brush 20 is mounted by means of the screw 19.

The terminal assembly 14 comprises an element 21 which is affixed to the fuse tube 13 by the screw 22 and which is provided with an opening 23 for receiving the laterally extending portion of a switch stick. Pivoted to. the. structure 21 by the pin 24 is a contact element 25 having contact surface 26 arranged to engage the contact brush 20 and having a surface 25a which normally engages the surface 21a of element 21. Mounted at the lower extremity of the contact element 25 is a fuse ejector element 27 which pivots about a center which is coaxial with the trunnions 28 extending outwardly from the element 25 and disposed in slots 18 in support elements 15a. Ejector element 27 is provided with a shoulder which engages a part of element 25 to prevent counterclockwise rotation and is biased by a spring 29 for rotation in the clockwise direction. The parts are maintained in the positions represented in Fig. 1 by means of the fuse conductor 30 which is drawn through the lower end of the fuse tube 13 and afiixed to the contact element 25 by means of the terminal screw 31.

Terminal assembly 12 as can be seen from Fig. l is afiixed to the upper extremity of the fuse tube 13 by means of a screw 32 and is provided at its left-hand extremity with a contact portion 33 arranged to cooperate with the contact brush 11. Furthermore the assembly 12 is provided with an upwardly extending portion 34 which acts. as a latch when disposed to engage the latching surface 10 of the hood 7. The right-hand extremity of the terminal assembly 12 is provided with an extension 35 having an opening 36 therein for receiving a switch stick whereby to manipulate the cutout manually in known manner. The upper end of the terminal assembly 12 is closed by means of a cap member 37.

The circuit through the structure shown in Fig. 1 comprises conductor 5, terminal bracket 4, brush contact 11, contact element 33, the fusible element disposed within the fuse tube 13, conductor 30, contact element 25 of the terminal assembly 14, brush contact 20, terminal and conductor 16.

Upon the occurrence of an overload or fault condition the fusible element disposed within the fuse tube 13 is ruptured and since the fuse tube 13 is constructed of a material which emits gas when in the presence of an electric arc, the arc is extinguished by expulsion action in known manner. Once the fusible element is melted the ejector element 27 under the action of spring 29 rotates in a clockwise direction about its pivot 28 and forces the conductor 39 and parts of the fusible element connected therewith downwardly and outwardly of the tube 13. Since the shoulder a of the element 25 is no longer maintained in engagement with the surface 21a of the element 21 by the conductor 30 and the fusible element, the pivot 24 begins to describe an arc in a clockwise direction about the trunnions 28 due to the action of gravity on the cutout and to the bias of brush contact 20. Upon completion of suflicient arcuate travel of the pivot 24, the surface 34 of the terminal 12 disengages the latch 19 of the hood 7 and the whole cutout swings in a clockwise direction about the trunnions 28 to form a gap in the circuit controlled by the cutout as is well known in the art.

For fault or overload currents which are below a predetermined value the above described operation takes place and the expulsion action is entirely through the lower end of fuse tube 13.

Power fuses and cutouts are called upon to interrupt a wide range of currents. 1f the device is constructed so that the expulsion action is sutficient to interrupt currents of a low order of magnitude, it is likely that the amount of pressure gas given off from the inner walls of the fuse tube 13 will be so great as to cause damage to the apparatus when currents of a high order of magnitude are interrupted. In order to protect the apparatus from damage when interrupting heavy currents, it has been the practice to provide supplementary pressure relieving means which is effective to aid in exhausting the pressure gas to atmosphere only when heavy currents are interrupted which cause high pressures to be developed.

In accordance with this invention the improved pressure relieving means as shown in Fig. 2 is provided. As has already been explained the arrangement of Fig. 2 is an enlarged cross-sectional view of the terminal assembiy 12 of Fig. l and parts associated therewith. As is shown in Fig. 2 terminal element 12a is a unitary member and is provided with a main passage 38 in which is affixed by threaded engagement at its lower extremity the upper end of the fuse tube 13 and in which the cap member 37 is affixed at the upper extremity thereof by threaded engagement. An inwardly projecting flange 39 is disposed in the main passage 38. An auxiliary passage 4t'i communicates at its left-hand end with the main passage 38 and is open to atmosphere at its right-hand end. Also disposed within the main passage 38 is a closure means 41 which may take the form of a fuse head as shown in Fig. 2. Aflixed to the closure member 41 is the fuse conductor 42. The closure means or button head 41 is biased into engagement with the inwardly extending flange 39 by means of compressional spring 43 which is aflixed at its upper end to the cap member 37 by having an enlarged portion 44 thereof disposed within a groove 45 formed within the cap member 37. As is clearly shown in Fig. 2, the cap member 37 is provided with an inwardly extending sleeve 46, the lower extremity of which is spaced from the button head 41.

When currents below a predetermined magnitude are interrupted the spring 43 maintains the button head 41 securely in engagement with flange 39 so that no appreciable amount of gas escapes via the upper end of tube 13.

Upon the occurrence of an overload or fault condition resulting in a current magnitude which is above a predetermined value, pressure gas formed within the fuse tube 13 forces the fuse button head 41 upwardly against the biasing action of the spring 43 thereby to allow a portion of the pressure gas to escape upwardly from within the fuse tube 13 through the lower end of main passage 38 and the exhaust or auxiliary passage 4-0 to atmosphere, it being understood that a portion of the gas escapes through the lower end of tube 13. When the button head 41 moves upwardly, being of larger diameter than the inner diameter of the sleeve portion 46, it engages the sleeve 46 so as to isolate and shield the spring 43 from the heat of the exhaust gases. This feature of the invention is of importance since the ex= tremely high temperatures developed during an interrupting operation would otherwise tend to alter the charac teristics of spring 43 and would result in nonuniform operation of the device. Furthermore it will be observed that the spring pressure exerted by yieldable spring 43 can be adjusted by simply rotating the cap member 37 and in this way the pressure within tube 13 at which the button head 41 moves away from the inwardly extending flange 39 can be varied as desired. Of course a set screw or other means (not shown) could be used to hold securely the cap member 37 in any desired position. Furthermore the maximum travel of the button head 41 prior to its engagement with the lower extremity of the inwardly extending sleeve 46 can also be varied by rotary adjustment of the cap 37. Since the button head 41 is confined by the structure shown in Fig. 2 and is not allowed to escape, it is prevented from causing possible damage to operating personnel or to nearby apparatus. An are drawn between the lower surface of the button head 41 and the upper surface of the flange 39 may fuse these surfaces and after extinction of the main are within tube 13 these parts may become welded together when the button head is moved back into engagement with the flange. If this happens the button head may readily be separated from the flange by means of a screw driver or other similar implement inserted through the auxiliary passage 40. 7

While we have shown and described a particular embodiment of the invention we do not wish to be limited thereto and intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric terminal assembly comprising an element formed of conducting material and having a main passage therein, an auxiliary passage formed in said element with its inner end in direct communication with said main passage and with its outer end in communication with atmosphere, closure means formed of conducting material and disposed in said main passage and normally positioned to one side of said auxiliary passage to prevent communication between one portion of said main passage and the inner end of said auxiliary passage, said closure means normally being in engagement with a part of said element thereby to establish a path for the flow of electric current, and yieldable biasing means urging said closure means toward its normal position, said closure means being movable in said main passage against the action of said biasing means toward the other side of said auxiliary passage in response to pressure in said one portion of said main passage which is above a predetermined magnitude.

2. An electric terminal assembly comprising an element having a main passage formed therein, a portion of said element constituting an inwardly projecting metallic flange in said main passage, an auxiliary passage formed in said element with its inner end in direct communication with said main passage and with its outer end in communication with atmosphere, metallic closure means in said main passage normally positioned adjacent to and in engagement with said flange and to one side of said auxiliary passage to establish a path for the flow of electric current between said flange and said closure means and to prevent communication between one portion of said main passage and the inner end of said auxiliary passage, and yieldable biasing means urging said closure means toward engagement with said flange, said closure means being movable in said main passage against the action of said biasing means toward the other side of said auxiliary passage in response to pressure in said one portion of said main passage which is above a predetermined magnitude.

3. A fuse terminal assembly comprising a terminal element having a main passage therein, an auxiliary passage formed in said element with its inner end in direct communication with said main passage and with its outer end in communication with atmosphere, closure means in said main passage normally positioned to one side of said auxiliary passage to prevent communication between one end of said main passage and the inner end of said auxiliary passage, a cap member closing the other end of said main passage and having an inwardly extending portion, and biasing means urging said closure means toward its normal position, said closure means being movable in said main passage against the action of said biasing means toward the other side of said auxiliary passage and into engagement with said inwardly extending portion of said cap member in response to pressure in said one end of said main passage which is above a predetermined magnitude.

4. A fuse terminal assembly comprising a terminal element having a main passage therein, an auxiliary passage formed in said element with its inner end in direct communication with said main passage and with its outer end in communication with atmosphere, closure means in said main passage normally positioned to one side of said auxiliary passage to prevent communication between one end of said main passage and the inner end of said auxiliary passage, an inwardly extending sleeve in the other end of said main passage, and spring means disposed within said sleeve for biasing said closure means toward its normal position, said closure means being movable in said main passage against the action of said spring means toward the other side of said auxiliary passage and into engagement with said sleeve in response to pressure in said one end of said main passage which is above a predetermined magnitude.

5. A fuse terminal assembly comprising a terminal element having a main passage therein, an inwardly projecting flange in said main passage intermediate the ends thereof, an exhaust passage in a wall of said main passage on one side of said flange, a fuse element having a head portion normally in engagement with said one side of said flange and with a link portion extending into said main passage on the other side of said flange, and biasing means for normally maintaining said head portion in engagement with said one side of said flange, said biasing means being yieldable in response to pressure in said main passage on said other side of said flange to allow said head portion of said fuse to move out of engagement with said flange to allow the pressure to escape to atmosphere through said exhaust passage.

6. A fuse comprising a fuse tube, a terminal element having a main passage therein, an inwardly extending flange in said main passage, said terminal element being aflixed to one end of said tube with said main passage disposed in coaxial relation thereto and with one side of said flange in engagement with said one end of said tube, an exhaust passage through a wall of said main passage on the other side of said flange, fuse element having a head portion normally in engagement with said other side of said flange and with a link portion extending through said flange and into said tube, and biasing means for normally maintaining said head portion in engagement with said flange, said biasing means being yieldable in response to pressure. within said tube above a predetermined magnitude to allow the pressure to escape to atmosphere through said flange and exhaust passage.

7. A fuse comprising a fuse tube, a terminal element having a main passage therein, an inwardly extending flange in said main passage, said terminal element being aflixed to one end of said tube with said main passage disposed in coaxial relation thereto and with one side of said flange in engagement with said one end of said tube, an exhaust passage through a wall of said main passage on the other side of said flange, a fuse element having a head portion normally in engagement with said other side of said flange and with a link portion extending through said flange and into said tube, a cap member secured in the end of said main passage remote from said tube, and a compression spring interposed between said cap member and said head portion of said fuse for normally maintaining said head portion in engagement with said flange, said spring being yieldable so as to allow pressure within said tube above a predetermined magnitude to escape to atmosphere through said flange and through said exhaust passage.

8. A fuse comprising a fuse tube, a terminal element having a main passage therein, said terminal element being aflixed to one end of said tube with said main passage in communication therewith, an inwardly extending flange in said main passage, an exhause passage through a wall of said main passage on the side of said flange remote from said tube, a fuse element having a head portion normally in engagement with the side of said flange remote from said tube and having a link portion extending through said flange and into said tube, a cap member closing the end of said main passage remote from said tube and having a sleeve portion disposed within said main passage, and a coiled compression spring disposed within said sleeve portion of said cap member and in engagement with said head portion of said fuse element, said spring being collapsible so as to allow pressure within said tube above a predetermined value to escape to atmosphere through said exhaust passage, said head portion of said fuse element and said sleeve portion of said cap member being effective to shield said spring from the heat of the are formed upon the melting of said fuse element.

9. A fuse comprising a fuse tube, a terminal element having a main passage therein, said terminal element being affixed to one end of said tube with said main passage in communication therewith, an inwardly extending flange in said main passage, an exhaust passage through a wall of said main passage on the side of said flange remote from said tube, a fuse element having a head portion normally in engagement with the side of said flange remote from said tube and having a link portion extending through said flange and into said tube, a cap member having a sleeve portion disposed within the end of said main passage remote from said tube in threaded engagement therewith, and a coiled compression spring disposed within said sleeve with one end thereof aflixed to said cap member and with the other end thereof in engagement with said head portion of said fuse element, said head portion being engageable with said sleeve in response to collapse of said spring.

10. A fuse comprising a fuse tube, a terminal element having a main passage therein, said terminal element being aflixed to one end of said tube with said main passage in communication therewith, an inwardly extending flange in said main passage, an exhaust passage through a wall of said main passage on the side of said flange remote from said tube, a fuse element having a head portion normally in engagement with the side of said flange remote from said tube and having a link portion extending through said flange and into said tube, a cap member having a sleeve portion disposed within the end of said main passage remote from said tube in threaded engagement therewith, said head portion of 7 said fuse element being larger in diameter than the inside diameter of said sleeve, and a coiled compression spring disposed within said sleeve with one end thereof aflixed to said cap member and with the other end thereof in engagement with said head portion of said fuse element,

said spring being yieldable in response to pressure Within said tube in excess of a predetermined magnitude to allow the pressure to escape to atmosphere through said exhaust passage and to cause said head portion to engage said sleeve so as to isolate said spring.

References Cited in the file of this patent UNITED STATES PATENTS Packard Nov. 1, 1898 Aldridge Mar. 11, 1913 B011 et a1. May 7, 1935 Lange Feb. 21, 1939 Parker et al May 20, 1941 Schultz Oct. 21, 1947 Linde et a1. June 20, 1950 FOREIGN PATENTS Italy July 11, 1929 

